Using on Canon MkII, I've found that my recently bought, little used Zuiko 21mm F2 has vignetting which never completely goes away with stopping down (no filters on!), although it reduces in size it gets sharper and more noticeable!

Here at F11

What are the recommended Alternatives? (I don't use this FL enough to warrant the expense or size of the Zeiss 21/2.8)

I have tried the Voigtlander 20mm F3.5, which has smoother vignette but the IQ is not good.

That much vignetting is barely noticeable and isn't really a problem is it? Especially if you shoot RAW. My Oly 28/2 vignettes much more than that at f8 and it takes a 1sec slider adjust to sort it out with no change in picture quality.

FlyPenFly wrote:
Try going outside and taking a real picture.
The only reason I'm posting this is because this is what it does whatever I take! (This is just a plain blue sky shot on mono!)
It is very noticeable and Canon DPP doesn't do vignette adjust for non native lenses.
Concerning the 17-40L, yes it is better I've tested it but was hoping for something smaller.
How good/bad is the Nikkor 20/2.8 AiS cf. the Voigt?

I'm guessing this is inherent to the lens. I don't have the 21/2, but I do have the 18/3.5 and it retains a vignette at all apertures as well.

The Oly's (imo) trade the excellent distortion for the vignetting ... just the nature of optics / physics of light, those who design less vignetting, will necessitate more distortion (or weaker corners) ... the wider you go, the tougher it gets ... choose your poison.

I've got both the Oly 21.3.5 and the Nikon 20/2.8 AIS, but neither are available for me to use atm ... but from memory both have more reasonable vignetting than your 20/2 is showing @ f11.

I haven't gotten around to it yet, but I figure I should make a vignetting action specific to each stop @ my Oly 18/3.5

Here's some from the Nikon 20/2.8 AIS ... I'm thinking these are f16, f11 & f8 ... but I didn't name the files right back then, so it's only a guess as these seem to be the least (sequential) vignette shots from the series.

FlyPenFly wrote:
How far from the infinity stop is actual infinity? Maybe the adapter is too thick?

Infinity is spot on.

I think Kent has it, which is why I askedfor alternatives!
Thanks for those of the Nikon 20mm F2.8 AiS Kent, they look very similar to my Zuiko, if not moreso, looks like it's a problem of this FL, I think I'll pass on the Nikkor too!.

Vignetting, distortion, resolution ... you can have any two, but not all three when it comes to WA/UWA. How much you are willing to trade of each is pretty subjective, with a lot of people opting to go with a mustache distortion like the Zeiss or Tamron's do.

The one thing I found @ my Nikon vs. Oly 21/3.5 (not shown here) was that the Oly had more even sharpness across the board and the Nikon a bit more centrally sharper/ softer corners.

Generally speaking ... the Zeiss is considered "The King" and the Oly 21/3.5 is good alternate choice for the $$$ diff. The Zeiss has mustache distortion and is a beast, but retains it status even so. I like the Oly for it's even sharpness into the corners and its $$$ / size diff, as well as the slightly lower contrast (than the Nikon 20/2.8 AIS) can be useful in high DR scenes.

Those were raw-jpgs that had been processed & down sized via PS way back when.

BTW ... if you are looking to avaoid vignetting in the WA/UWA camp ... the newer Tilt-Shift lenses have larger image circles that pretty much obliterates vignetting, have superb distortion control and excellent resolution and smooth tonal transition ... albeit a touch less contrasty (easy to bump in post) as the projection does spread out it little bit more.

Size, weight & $$$ all go up accordingly, but for WA/UWA ... my 24L TS-E II is virtually flawless @ distort/vignette/resolution. I can only image the new 17L TS-E is likewise benefitted by the larger image circle.

If the size isn't a problem, I would really recommend saving up for the Zeiss. It is just a brilliant lens, and you can probably save a bit of money by getting the ZF (1) version. What will the Olympus 21/2 get you?